5.56 Small arms ammunition

ABSTRACT

Described herein is a round of ammunition for firing from a gun having a rifled barrel, especially a small arms weapon. The round comprises a body core ( 7 ) which has a plurality of knurl lines ( 9 ) and associated grooves ( 6 ) formed over a portion of the body core ( 7 ). Jacket material ( 11 ) is provided over the body core ( 7 ) such that the inner diameter ( 10 ) of the jacket material ( 11 ) makes contact with the knurl lines ( 9 ). During firing of the round, the jacket material ( 11 ) deforms into the grooves ( 6 ) formed between the knurl lines ( 9 ) enabling the rifle engraving to take place with a substantially reduced axial force.

This invention relates to ammunition for use in a weapon having a rifled barrel, and especially to an improved form of projectile for small arms ammunition.

When a projectile is fired from a rifled barrel, the projectile must deform as it travels along the barrel so that material forming part of the projectile is forced into the spaces between the lands forming the rifling. This process is called engraving, and causes a spin to be imparted to the projectile by virtue of the longitudinal twist of the rifling.

The deformation of the projectile, its travel along the barrel effectively as a force fit to the rifling, the high linear acceleration imparted by the gun propellant on firing, and the consequent high rate of angular acceleration and associated force acting between rifling and projectile all contribute to substantial wear on the barrel.

If this wear rate can be reduced, substantial benefits follow, including increased barrel life, higher muzzle velocity and hence increased accuracy and lethality.

For this reason, low friction, readily deformable materials are normally selected for small arms bullets, for example lead. In order to increase the overall density of the bullet, it has also been proposed to use steel. However, steel is not readily deformable, and causes unacceptable barrel wear. On the other hand, hardness is a very desirable characteristic for the bullet material, in order to minimise nose tip ablation during penetration of hardened targets such as, for example, titanium/kevlar body armour. For these purposes, a Vickers Hardness of at least 550 (using a 10 kg load) is the minimum desirable.

In seeking to overcome these problems, it has been common practice to make a small arms bullet from a steel core, enclosed in a gilding metal jacket.

This latter solution is practical, but results in a bullet having a relatively expensive construction. This is a very significant disadvantage since small arms ammunition is consumed in large quantities, and the market for such ammunition is highly competitive.

In U.S. Pat. No. 5,686,693 there is disclosed a 7.62 mm bullet formed from a steel alloy, having a forward body portion whose diameter corresponds to that of the rifling lands of an associated gun, and a rearward body portion having a greater diameter, and provided with annular grooves. The body is provided with a coating which can be of copper. In use, the copper coating acts as a lubricant, and is less thick than the depth of the rifling. When fired from the rifled barrel, the rifling therefore cuts through the copper coating so that the steel body of the bullet is engraved by the rifling. In the disclosure it is stressed that the steel of the body must be soft, so as to permit this engraving to occur without undue barrel wear. The maximum value for the hardness of the steel body mentioned in the disclosure is 210 Brinell, which equates to a Vickers Hardness of 213, i.e. very much less than the desirable minimum value of 550 Vickers Hardness. As a result, the bullet disclosed in U.S. Pat. No. 5,686,693 will lack the desirable target penetration capability.

It would therefore be a considerable advantage if a way could be found to utilise steel or other metal having a Vickers Hardness equal to at least 550 (using a 10 kg load) as the principal component of a small arms projectile, while enabling the projectile to be engraved by the rifling and not introducing unacceptable friction or wear, and avoiding the expensive construction of applying a jacket to the projectile.

According to the present invention there is provided the combination of a gun having a rifled barrel and a round of ammunition; the rifling of the barrel comprising rifling grooves which are separated by lands extending helically along the length of the barrel; the round of ammunition comprising a projectile; the projectile having a body comprising at substantially cylindrical body comprising a plurality of extending splines or knurl lines producing a corresponding plurality of grooves along a section of the main diameter of the body; a deformable jacket means substantially surrounding a proportion of the diameter of the main body corresponding to the section of the main body comprising said splines or knurl lines; wherein the main body of the projectile is formed from a metal having a Vickers Hardness of not less than 550 HV, and the maximum diameter of said main body comprising said splines or knurl lines being substantially equal to or less than the minimum internal diameter of the weapon barrel.

Normally, the projectile will also have an ogival nose portion of the body forward of said forward body portion, although other forms are possible.

The main body of the projectile should normally have a diameter which is not greater than that defined by the roots of the grooves of the rifling. Upon engagement with the rifling the knurl lines or splines are designed to deform into the groove air gaps corresponding to said splines or knurl lines, and thus engaging with the lands, inducing spin in the projectile due to the twist of the rifling. This deformation gives the body an interference fit with the rifling so as also to provide effective obturation by restricting or preventing the escape of propellant gases past the projectile via the rifling grooves. The length and precise diameter of the body should be designed with these factors in mind.

Regard must also be taken to ensure that the force required to effect the deformation of the jacket material and to propel the projectile along the barrel is not excessive, and this is the reason why the diameter of the body should not normally be greater than that of the rifling groove. This force is substantially reduced by the presence of the air gaps between the knurl lines or splines allowing the material to deform into said groove air gaps during the passage of the body along the barrel.

The depth of said grooves of knurl lines should preferably be between about 1% and 10% of the nominal diameter of the projectile, and an optimum design may be between 2% and 6%.

The material selected for the projectile body will depend partly upon the function which the projectile is to perform, but in the case of High Performance Ammunition should not usually be below a Vickers Hardness of 550 HV.

For a warshot ammunition nature to be used in combat conditions, steel is a suitable material, as it is inexpensive and can be readily formed into the desired shape, eg. by a cold-forming process. Tungsten is another possible material because hardness is an important characteristic for target defeat, as are alloys of tungsten, and tungsten carbide.

The invention is particularly but not exclusively applicable to small arms weapons systems, having a nominal calibre of 20 mm or less, especially 9 mm or less.

The invention will now be described by way of example only with reference to the accompanying drawings, of which:

FIG. 1 shows a diagrammatic representation of a round of small arms ammunition incorporating grooves of knurl lines projectile for use in combination with a gun having a rifled barrel, in accordance with the invention; and

FIGS. 2A and 2B each shows a cross sectional elevation A-A through the projectile shown in FIG. 1, additionally depicting the envelope of said projectile.

As shown in FIG. 1, a small arms ammunition projectile 1, comprising a main body portion 2, a tip portion 3 and along the main body a plurality of grooves or knurl lines 4 producing corresponding splines 5 and air gaps 6.

The projectile body is of elongate form and is cold formed from steel having a Vickers Hardness of at least 550. It can subsequently be given a heat treatment to provide the desired hardness or other physical properties. The projectile comprises a body 2 of substantially cylindrical form.

Because of the substantial hardness of the projectile body material, the projectile is highly effective at penetration of targets such as titanium/kevlar body armour. Moreover, the hardness also serves to minimise ablation of the projectile tip profile, thus further contributing to its effectiveness in target penetration.

FIGS. 2A and 2B show representative cross sections A-A on FIG. 1. In FIG. 2A, the detail of the knurl lines 9 and associated ‘groove’ air gaps 6 of the projectile body core 7 is shown when the projectile body core 7 is located within surrounding jacket material 11. Similarly, in FIG. 2B, the splines 5 and associated ‘groove’ air gaps 8 of the projectile body core 7 is shown when the projectile body core 7 is located within surrounding jacket material 11.

When the body 9 and associated coating 13 passes from the gun chamber into the rifled part of the barrel, by virtue of its greater diameter, the jacket material 11 deforms into the corresponding groove air gaps 6, 8 corresponding to the splines 5 or knurl lines 9. The internal diameter 10 of the jacket material 11 should preferably be substantially equal to or less than the diameter of any rifling grooves (not shown).

The presence of the grooves 6, 8 facilitates the necessary deformation of the jacket material 11, thus enabling the rifle engraving to take place with a substantially reduced axial force. The fact that the jacket material 11 can deform into the grooves 6, 8 contributes considerably to a dramatic reduction in the axial force required for engraving to occur.

Therefore, despite the hardness of the material forming the main part of the projectile body, barrel wear from this factor is minimised.

It will be evident to the skilled addressee that all of these factors reducing the engraving force will also result in reduced barrel wear, higher muzzle velocity, and hence increased lethality and accuracy.

The projectile which forms part of the combination of gun and ammunition tile according to the invention is also considerably less expensive to manufacture than a corresponding conventional projectile in, for example, a gilding metal jacket.

The optimum design parameters for the projectile according to the invention can be determined by those skilled in the art, based on the teaching contained herein.

The invention is particularly but not exclusively applicable to small arms ammunition. In one particular example, the invention has been successfully applied to 5.56 mm gun and ammunition. 

1. The combination of a gun having a rifled barrel and a round of ammunition; the rifling of the barrel comprising rifling grooves which are separated by lands extending helically along the length of the barrel; the round of ammunition comprising a projectile; the projectile having a body comprising at substantially cylindrical body comprising a plurality of splines or knurl lines producing a corresponding plurality of grooves which extend along the length of a section of the main diameter of the main body; a deformable jacket means substantially surrounding a proportion of the diameter of the main body corresponding to the section of said main body comprising said splines or knurl lines; wherein the body of the projectile is formed from a metal having a Vickers Hardness of not less than 550 HV, and the maximum diameter of said main body comprising said splines or knurl lines being substantially equal to or less than the minimum internal diameter of the weapon barrel.
 2. A combination according to claim 1 wherein the projectile has an ogival nose portion of the body forward of said forward body portion.
 3. A combination according to claim 1 wherein the depth of said grooves is between about 1% and 10% of the nominal diameter of the projectile.
 4. A combination according to claim 3 wherein the depth of said grooves is between about 2% and 6% of the nominal diameter of the projectile.
 5. A combination according to claim 1 wherein the projectile body is made of a material selected from the group comprising steel, tungsten, alloys of tungsten, and tungsten carbide.
 6. A combination of gun and ammunition according to claim 1 wherein the diameter of the main body is less than or equal to the diameter defined by the roots of the said rifling grooves.
 7. A combination of gun and ammunition according to claim 6 wherein the diameter of the main body is substantially the same as the diameter defined by the roots of the said rifling grooves.
 8. A combination of gun and ammunition according to claim 1 wherein the diameter of the body portion is less than or equal to the diameter defined by the said lands.
 9. A projectile for use in a combination as claimed in claim 1; the projectile having a main body comprising a substantially cylindrical body portion, and a plurality of longitudinally extending knurl lines or splines resulting in corresponding grooves along said main body; wherein the body of the projectile is formed from a metal having a Vickers Hardness of not less than 550, and the maximum diameter of said main body comprising said splines or knurl lines being substantially equal to or less than the minimum internal diameter of the weapon barrel.
 10. A projectile according to claim 9 wherein the depth of the said annular groove is between about 1% and 10% of the nominal diameter of the projectile.
 11. A projectile according to claim 1 wherein the projectile body is made of a material selected from the group comprising steel, tungsten, alloys of tungsten, and tungsten carbide.
 12. A projectile according to claim 1 having nominal calibre of 9 mm or less.
 13. A projectile according to claim 12 wherein the said nominal calibre is 5.56 mm. 14 and
 15. (Canceled) 